This invention relates generally to orthopedic prostheses and more specifically to an acetabular liner extractor for use with a prosthetic acetabular cup.
Ceramic-to-ceramic and metal-to-metal bearing surfaces have been commonly used in orthopedic prostheses. More specifically, first generation acetabular prosthetic devices were originally constructed with monoblock components. However, in the mid-1980's, modular inserts were introduced which employed a bearing surface made from one material while the portion in contact with the patient's bone was made from a dissimilar material. One such example used an alumina liner in a titanium shell. The alumina liner and titanium shell were connected by a self-locking Morse taper. Such tapered ceramic liner and titanium shell combinations are well known in the industry and have been sold since 1988 by Joint Replacement Instrumentation Ltd. as the FURLONG.RTM. H-A.C Screw-In Cup. Another well known ceramic liner and metal shell acetabular cup assembly, having self-locking tapered mating surfaces, was sold by Ceraver of France and disclosed in "The Use of Dense Alumina-Alumina Ceramic Combination in Total Hip Replacement," Journal of Biomedical Materials Research, Vol. 22, pages 1203-1232 (1988), authored by P. Boutin, P. Christel, J. Dorlot, A. Meunier, A. deroquancourt, D. Blanquaert, S. Herman, L. Sedel and J. Witvoet.
Various removal instruments have been employed in an effort to remove the liner from the shell. One such instrument was designed to slide down a thin cavity between the shell and liner and wedge the liner out from the back side. This instrument has enjoyed limited success as it is fairly small in cross-section and the force required to separate the shell and liner can deform or fracture the instrument without separating the components. Another instrument utilized a pipe-like member that rests against the shell without touching the liner; a hammer blow was then applied to the pipe-like member whereby the resonant frequency, vibration or impact force created in the shell loosens the taper connection.
Furthermore, U.S. Pat. Nos. 5,413,603 and 5,282,864 disclose a tapered liner and shell which incorporate set screws disposed in slots in the liner and shell which act against notches to disengage the locking taper. Other notches are employed for engagement by a tang of a loosening instrument to pry the liner from the shell. These slots and notches require additional machining of the liner and shell thereby increasing manufacturing costs and reducing the amount of contact area of the taper. Moreover, this off-center prying manner of removal causes bending forces between the liner and shell which appears to make disassembly somewhat difficult.